Photographic material



May 13, 1941. L. POLLAK 1 2,241,519

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Patented May 13, 1941 rno'roonsrmc MATERIAL Louis Pollak, Altrincham, Cheshire, England Application May an, 1931, Serial No. 143,704

- In Great Britain May '23, 1936 'iClalms.

My invention relates to colour photography and in particular to colour photographic negative and positive records, principally for colour motion pictures, on the subtractive principle of the kind comprising two or three superposed emulsion layers on a Celluloid or other suitable support, with or without interposed light filters. The invention also includes the method of producing and processing the photographic material.

In the productionof colour photographic records it is known to employ additive and subtractive processes. The former employ a carrier of Celluloid or other transparent material provided with red, green and blue grains in mosaic or geometrical patterns, upon which a panthe dimculty of eliminating the grain effect in the projection on the screen and finally the impossibility of duplication of the original.

In the known subtractive processes three basic I colour (or two basic colour combinations) separation negatives have to be made by exposure through suitable filters, which negatives may be made adaptable for still photography or cartoon films, but for moving objects such as generally formthe subject matter of cinematography, the simultaneous exposure of three separation negatives can only be effected with a camera specially constructed for thispurpose with splitbeam device and 'bi-pack. Stereoparallax and double image reflections are dimcult to. overcome, fully opened aperture and excessive light, so very detrimental to the comfort and the acting qualities of the performers, are required, while the definition of bi-pack images". thrown on the screen at 200 to 300 enlargement results in unsharp outlines and the need to employ a fourth, i. e. black screen image.

The printing of the positives is slow and irregular, with consequently high waste production and indefinite production costs. Where print matrices from the three (two) separation negatives are made, and the positives printed byimbition, only images of a fairly large size can be successfully mader For cinema film purposes the images are too small and the unavoidable transgression in the registration of the three (two) dye images during printing seriously affects the fine outlines and gradation of the combined colour image when magnified on the screen. The successive three (two) printing processes from matrix to positive image carrier demand a very precisely working machine and still more perfect working material. Negatives, matrices, positive materials passing through a number of chemical and mechanical processes are bound to shrink or stretch. Matrices o'r wash-out-reliefs according to the Koppmann patents (pyrocatechine-developer without sodium-sulphite) or by bromoil bleaching are used, and as dye medium acid dyestuffs, which are irregular in their application,-

in as much as the dye bleeds and its very slow transfer does not take place without remainder,

resulting-in positives, not two of which are alike in colour gradation. The transfer of basic dyestuffs is quickerand more complete, but according to the capillar principle the matrix is bound to carry loose dye in the fine crevasses if the image, which through the pressure applied in printing will appear on the positive in blurred outlines, creating around the white objects an aureole so disturbing to the eye. The harmonising of colours, their concentration, their printing time, the correct light exposure of the negatives, the indefinite gamma valuesof the negatives and print matrices are factors of such intricate nature, that the slightest divergence of any of them from the theoretically perfect prescription will lead to considerable waste, and therefore unprofitable production. To avoid these difiiculties systems have been evolved, in which a photographic colour element carries a plurality of superimposed layers sensitised to different colours, such elements' being exposed so as to obtain. images in the respective layers corresponding to the colour sensations to which the respective layer is sensitised. Quite a number of systems based .on this principle have; been patented with the uncertainty in the control' of the various processes involved, more particularly the limitation of the penetration to each individual layer. the developing and bleaching of each layer and finally the removal of the silver halide from these layers, none of which will permit perfectly coloured images to be obtained. These images are not fast to light, they bleach out easily, and are affected by acids, even such weak reactions as the carbon-dioxide contained in the air.

There are further the reversal processes, wherein the colours are contained in the layers, between which a thin clear insensitive gelatine film dyed to act as a filter is placed, and wherein the images are decolorised and reconverted to silver salt. images, which are subjected to a colour de- 'to estimate correctly the time of developing and bleaching and removal of silver within the first and second top layers without affecting the lowest layer. Colour corrections are impossible and the slightest variation'in the exposure will affect correct colour rendering. Finally such processes do not permit the production of positives and are therefore restricted to amateurand mainly substandard films.

According to the present invention a layer consisting of a silver halide gelatine emulsion sensitised to part of we whole visible spectrum,

or two such layers, sensitised to different parts of the spectrumrand the gelatine of which is so hardened as to be insoluble in warm water, has or have superposed another layer of silver halide gelatine emulsion sensitised to another part of the whole visible spectrum in which the gelatine is not hardened, in order to permit the formation of a wash-out-relief in accordance with the'silver image produced, or is only hardened to the extent of still being soluble in warm water, this layer (or layers) containing a dyeforming substance enabling the formation of an image insensitive to the influence by the silver image, in a dyeor colour substantially complementary to that part of the visible spectrum to which this layer is sensitized. Alternatively one of'the layers of silver halide emulsion hardened and sensitised for one part of the whole visible spectrum may bearranged on the other side of the Celluloid or other support or on a separate element which is exposed simultaneously and in close contact with the double layer element recording two parts of the whole visible spectrum.

The negative is exposed in an ordinary camera and after processing is printed on a positive of similar construction, .the negative recording the three primary colours, while the positive will record the three colours supplementary to those of the negative, for which a fine grain emulsion of less sensitivity-is recommended. Such positive record may, however, be used for reproductionof negatives produced according to other methods, in every instance permitting the ordinary contact or optical printer to be employed.

The invention will now be more particularly described with reference to the accompanying drawing, wherein the same reference letters or characters refer to the same thing or part throughout the several views and in which:

Figure 1 is a flow-sheet of. a section of a film element wherein two emulsion layers'are superposedon one film base or support, in the first view before exposure, in the second view after exposure and development and in the third view after further processing; a

Figure 2 is a cross section of a film element having two layers of emulsion on one side of the film base or support and one layer of emulsion on the other side;

Figure 3 is a flow-sheet of a cross section of a film element corresponding to Figure 1 with the addition of=a third emulsion layer on a separate film element, the first view showing the v element before development and the second view the same element after development; V Figure 4 is a section of a modified film eleimposed upon layer B is the second gelatine-' silver halide layer C the gelatine of which is not hardened and is soluble in warm water, and this layer contains an agent capable of precipitating a dyestuff or an insoluble'colour-former from which in the later process through colour synthesis (coupling) a suitable dye image is formed.

Having exposed this negative element in an ordinary camera, it is desensitised, developed, fixed and washed, resulting in black silver images L and M in the respective layers as indicated in the second view of Figure 1. solution of copper sulfate, potassium-bromide and chromic acid will bleach the silver images and harden the gelatine in correspondence with the silver image in layer C. The film is then bathed in warm water and such parts of the gelatine and the dye forming substance in layer C which have not been hardened will thereby be removed and a wash-out-relief image created.

The film is next placed in a solution containing the required dye coupling compound resulting in the formation of a dyestufi image. If, for instance, the emulsion in'layer C contains an azo dye forming component,.such as the water insoluble salts of naphthol-, or naphthaleneor naphthylamineor benzidine-sulfonic or disulfonic acid compounds, a diazo-compound will convert the bleached image into a dyestuff image, for example, if amido-naphthol-disulfonic acid H or the water-insoluble salts of the same form constituents of the emulsion, a cliazotised solution of dianisidine produces a blue dye image. Alternatively if the diazo coupler is contained in the emulsion, the dyestufi image will be obtained by reaction in a solution of the respective azodye forming compound. Layer B, being without a colour forming .or coupling component, will remain unaffected, while both layers retain the bleached silver and copper halide images. These silver and copper halide images are converted into mordant dye images 'by applying a solution of thiocarbamide and a thiocyante, such as ammonia thiocyante and subsequently dyed in any colour with a basic dyestufi.

It is not necessary for layer C to contain strictly the red and the blue part colour. The blue part colour and the red part colour may be created by combining a blue-green with bluishred, and this measure is made use of, amongst others, in the present invention. In both layers the mordant images are dyed bluish-red, for instance the rhodamine-B. In the outer layer C the bluegreen azo-dyestufi is present, so that by the mixing ofi the former with the bluish red toning of the rhodamine-B the blue part colour image P in layer C and the red part colour image R in layer B are produced, as indicated in the third view of Figure 1.

The method of the present invention may be applied to more than two layers, and its processing can be simplified by combining some of the operations into one, for instance according to the following examples:

A bath in 8.

1. The first development can be carried through, instead of with the'usual known developers, with a so-called tanning developer.

without- (pyrocatechin with alkali (NaOH), scdium-sulfite), thus eliminating the bleaching bath of copper sulfate, potassium bromide and chromic acid.

. spectrum (Figure 2), is used. The lowermost 2; The dye-coupling or colour-forming compound necessary to form the dyestuif image with l 3. The development of the silver images may be done directly by means of a colour-developer, for instance, para-amino-dimethylanilin, wherein the respective dye-coupling component is added to the emulsion, which is of particular advantage, when elements having three superposed emulsion layers on one side are used.

4. The silver images may be converted by way of a chemical toning process, for instance with vanadium salts into yellow toned metal compound images. As the silver halide content in the emulsion of layer B is to behigher than in layer C, a deep-yellow part-colour image will result, while the image in layer C with a smaller silver halide content just sufiicient to permit the formation of the wash-out-relief, will appear only slightly yellow-toned, which toning combined with the blue azo-dyestuifin that layer forms the bluish-green image. of the dyestufi image depends upon the quantity of dye-forming substance in the emulsion and not upon the silver halide content, the smaller percentage of silver halide in layer C will not impair the correct colour representation.

5. Instead of azo, di'azoor other components capable of'forming a dyestuff by way of colour synthesis in the emulsion of layer C the latter may contain ingredients which precipitate dyestuffs as colour lakes or salts insoluble in water. For instance, if a calculated quantity of barium carbonateis added to the emulsion in layer C and such layer is bathed in a solution of a dyestuff of the sulfonic-acidgroups, chemical reaction will cause the formation of the insoluble barium salt of that dyestufi. Since the barium content and not the amount ofsolute in the dyestufi solution is responsible for the density of the dyestuff image, the dye bath and warm water bath may be conveniently combined.

6. In place of dyestuff-precipitating reagents, precipitating metal compounds, such as insoluble complex acids, phosphotungstic acid, antimonictungstic acid, silicotungstic acid and the like according to British Patent Specifications Nos. 344,365 of September 12, 1929; 353,819 of June 24, 1930, and 430,823 of June 20, 1935,. may

be added to the emulsion of layer C.

7. Alternatively stable leuco compounds, esters of dyestuffs, such as benzoylacetic-, acetoaceticor cyanocetic esters, pyrazolone and others may be used, while the'oxydation and warm water bath may be combined.

According 'to one useful modification of this invention, a film element having two superposed As the density layer B is sensitized'with for instance, thiocyanin or thiopseudocyanin or' erythrosin for yel low and green rays and the gelatine is hardened 'to withstand warm water superposed upon this layer, preferably with an intervening filter .layer,is another layer C, containing an insoluble azo-dye-forming component, sensitised with, for instance, naphtocyanin for yellow and red rays and with the gelatine not hardened, so as to be soluble in warmwater. On the reverse side of the film element A is arranged an ordinary gelatino-silver halide emulsion layer D which is hardened and only sensitive to blue rays, being preferably poor in silver and'transparent. f I

After exposure in an ordinary camera, the film is desensitised, developed, fixed and washed. A solution of copper sulfate, potassium bromide and chromic acid will turn the black silver images intO copper images and harden the developed'portion of the gelatine. The film then passes into a bath of warm water of to C., in which the unhardened gelatine and the dyeforming component are removed and a washdine, to form the blue-green dyestuif by reaction with the azo-dye-forming component, for

instance, amido-naphthol disulfonic acid-H, is

contained in the next following bath. In the next stage the film is placed in a solution of thiocarbamide, ammonium thiocyanate and glacial acetic acid, whereby the bleached copper images are converted into mordant dye images. The film is then subjected to a' waterbath, after which it is placed in a solution of rhodamine-B with a slight addition of acetic acid, thereby tuning the mordant dye images intensely bluishred. After anotherwaterbath, the film is ready to pass into the drying chamber.

The two superposed layers containing two. of

the three part-colour images, the red and the blue, are thus automatically formed, while the image in layer 1) on the other side of the base or support, intended for the yellow part image, is also red and as a further process in the developing machine the surface of the side carrying the emulsion layers B and C of the dried film is varnished for protection.

In another'bath an oxidant, for instance a weak solution of potassium permanganate with a slight addition of sulfuric acid, removes the red dyestuif of the mordant image in layer D. The film is then clarified in a waterbath and in a successive toning bath containing a yellow basic dyestuff, such as acridine-yellow, thiofiavin T (Schultz 6th ed. No. 618) and the like the mordant image in layer D is dyed yellow.

According to another modification of the invention, a film element having superposed two emulsion layers on one side, each sensitive to the colour sensations of one part of the visible spectrum, is exposed in an ordinary camera simultaneously and in close contact with a separate film element carrying only on gelatine-silver halide emulsion sensitised to the colour sensations of the remaining part of the visible spectrum as shown in the first view of Figure 3. The lowermost layer B of the double-coated element contains a elatine-silver halide emulsion hardened to withstand warm water, sensitive to screening dyestufi. superposed on layer B is layer C the gelatine-silver halide emulsion of which is not hardened andtherefore soluble in warm-water, sensitive to green and yellow rays andcontains an insoluble azo-dye-foijming component, such as an insoluble salt 'of-naphthol or naphthaleneor napthylamineor benzidinesnlfonic or disulfonicacid compounds, which by coupling with a diazo compound is capable of forming a reddyestufi image. Alternatively, if

the emulsion is sensitised for. yellow and red ,rays, a blue dyestuif image may be formed as "previously described. The .silver content in the emulsions of both layers is so chosen as to permit the formation of a weak silver image in the wash-out-relief of layer C. In place of the amcomponent for the. colour synthesis in layer C precipitators (lake formers) for dyestuifs or the insoluble lake combination of a leuco dyestuif mays-be used as previously stated. 'Ihe separate film element S, the emulsion of which is sensitive to either red and yellow or green and yellow, whichever colour sensations are not provided for in the double coated element, is developed like any ordinary black and white film (second view of Figure .3) its black silver image being converted into a mordant dye image by any known method and dyed with basic dyestuff either red or blue as required to complete the colour range of the visable spectrum. As the sil- 'ver halide emulsions, in the front double-coated film element are nearly transparent owing-to their limited: silver-content, the image of the black orseparate film.'element Swill be sharply outlined.

In a further modification of this invention the exposed film element carrying the two latent images in layers B and C is desensitised, developed and fixed inthe tubular developing machine. After a tanning bath, the film passes into a warm waterbath to which the diazo coupling yellow basic dye. Layer B now records the yellow part-image, while the mordant image in layer C, though slightly affected by the staining with the. yellow basic dye, will register either the blue or red part colour, whichever was chosen to be produced in the above described colour synthesis. The separate film element, which is to provide the third part colour image, is treated asabove described and its resulting mordant image dyed with basic dyestufi in the part colour not represented in the double coated film element. When placedin register, the two films willshowthe correct' three part colour negative, covering the whole of the visible spectrum. Alternatively, in place or the separate element processed as above, a print copy maybe made from it after development and fixing, which is converted into a washout-relief image and used as a print matrix, 1. e.

dyed in the required part colourand this dyestufi. image transferred by imbibition upon one of the gelatine layers of the'double coated film element, thereby completing the full range of the part c01- ours or the visible spectrum on one element.

2,241,519 blue rays and conveniently containing a yellow.

For reproduction in natural colours complementary to the negative record a positive element carrying three layers of fine grain gelatine-silver halide emulsion of rather less sensitivity than that selected for the negatives, superposed on one side (Figure 4) is provided, the construction of which maybe conveniently arranged as follows; On a film or other transparent support is placed a hardened gelatine-silver halide emulsion layer B, which is only sensitive to blue rays, for instance a silver bromide or bromide-chloride emulsion, containing a yellow filter dyestufi or alternatively a yellow filter between layers B and C. superposed upon layer B is layer C which consists of a gelatino-silver halide emulsion highly sensitised to green or red and hardened. Above layer C is arranged layer D containing a gelatino-silver halide emulsion not hardened, highly sensitised to red or green, whichever of the colour analysis is not used in layer 0 and an azo-dye forming component or dye precipitator as previously described.

The duplicating process from the negative colour records produced according to the invention, with theaid of an optical or contact printer, as used for ordinary black and white printing, may be conveniently. carried out as follows: In the first part of that process, the negitive colour record or record is or are projected through a strong yellow filter, such as tartrazine (Exposure Multiplication Factor 4) upon the positive element, whichwill produce latent images in layers C and D, without afiecting layer B. These latent images are processed in a tanning developer, such as pyrocatechin and alkali (NaOH),

without sodium ulfite, resulting in black silver images in each of the layers, of which the image in layer D appears tanned. In the subsequent warm water bath, to which may be added the diazo coupler or, if a precipitator is present in the emulsion of layer D a dyestufi, the developed and tanned image of layer D is converted into a dyed relief image. The film is now bathed in a solution of copper sulfate, potassium citrate and potassium ferricyanide, which turns the black silver images 'into mordants and is subsequently dyed in the required colour with a basic dyestufi, for instance, if dyed with rhodamine-B (Schultz 6th ed. No. 573), bluish-red images will appear in layers C and D. By further treatment in a bath containing a suitable diazo-compound the azodye forming component in relief image of layer D will form a. blue-green azo-dyestuif image. Thus in efi'ect the layers C and D together record the blue and red part colour images. The negative, colour record is now projected upon the positive element through a blue filter. Once more-developed a black silver image will appear in layer B, which may either be toned in a bath of vanadium chloride, acetic acid and potassium term-cyanide, or immediately after exposure treated in a yellow dye developer. The remaining silver halide in the three layers is now fixed out. a

This positive processing may be reversed in its order by the projection through the blue filter being applied first and the resulting latent image in layer B developed and toned yellow in the manner described above. The projection through ayellow filter follows on, with subsequent treatment and dye image formation in layers C and D as described above, in conclusion of which the silver halide in all the three layers is removed in a fixation bath. I

Instead of using the negative colour record by way of example.

produced according, to this invention, negatives obtained by other known processes, particularly those known under the registered trade-marks Dufaycolor and Finlaychrome, may be duplicated upon positive elements in accordance with this invention, whereby the reseau or screen e1- fect characteristic upon such negatives produced' by the additive principle will be eliminated in the positive images, which, being dyestufl' images, are entirely free from grain and therefore do not record the screenefiect oi the negative.

In order to avoid the use of the complicated and expensive colour cameras with beam splitting device or reflecting mirrors for the .production of colour separation negatives, the negative colour recordelement according to this invention may be adopted. In this case the usual dye-transfer relief images are extracted from the exposed and processed negative and the printing process on a positive carried out by the method well known under the registered trademark Technicolor or any other known imbibition process.

The invention is not limited to the construction and treatment of the film described herein It may be applied to other photographic elements such as, plates and other transparent material. Films described in this invention may carry a sound track. 7 Various changes may be made in the details disclosed in the foregoing specification without departing from the invention orsacrificing the trum, the gelatine in this layer being so hardened as to be substantially insoluble in warm water, while in another of said layers, sensitized to another part of the spectrum, the gelatine is soluble in warm water and the silver halide content is smaller than in said first-mentioned layer so as to permit after normal exposure only the formation of aweak silver image by a developing treatment which produces a strong silver image.

in said first-mentioned layer, these two layers being attached in superimposed relation on one side of said support wlth'the soluble layer outermost, and acolour forming substance in said soluble layer enabling the formation of an image, in a colour substantially complementary to the part of the spectrum to which this soluble layer is sensitized.

2.;.The photographic material of claim 1, in

which another insoluble emulsion layer is arranged between the soluble and the insoluble layer mentioned. a

3. The photographic material of claim 1, in which another insoluble emulsion layer is arranged on the second side of the support.

4. The photographic material of claim 1 in combination with another insoluble emulsion layer, arranged on a separate support, in close contact with the soluble layer of the first support. 5. The photographic material of claim 1, in 

